Temperature data taken over the Izu Ridge during 1964–1986 were analyzed to present the mean temperature structure and the mixed layer in the Kuroshio Region. Since the Kuroshio radically changes its position over the Izu Ridge, in order to construct the rational mean fields, we made composite analyses of the data using a coordinate with its origin at the Kuroshio axis. In the southern part of the Kuroshio axis, the 15 and 12°C isotherms lie at depths of about 400 and 550 m, respectively, in all months analyzed. These depths are shallower by 250 m than those of the Gulf Stream Pegasus section at 73W (Halkin and Rossby, 1985). This difference is attributed to that of layer thicknesses of the Subtropical Mode Water in the Kuroshio system and the 18°C water in the Gulf Stream system; layer thickness of the Subtropical Mode Water is thin, while the 18°C Water is much thicker. Seasonal variations of the mixed layer temperature and thickness were presented. Wintertime thicknesses are larger by a factor of two than those previously presented by Bathen (1972) using a simple geographical average for the North Pacific. There is a weak inverse correlation between the mixed layer temperature and thickness for both February and April; increased thickness of about 40 m correspond to a temperature decrease of 1°C for both months. Time series of anomalies of mixed layer temperature and thickness for February and April were described.